1. Field of the Invention
The present invention is directed to a gearwheel which can be used, for example, as a planet wheel in a planetary gear train in a torsional vibration damping arrangement for the drivetrain of a vehicle.
2. Related Art
FIG. 1 shows in a fragmentary longitudinal section a torsional vibration damping arrangement 10 which is configured to be positioned in the drivetrain of a vehicle. The torsional vibration damping arrangement 10 comprises an input region 12, which is to be connected by screws, for example, to the crankshaft of an internal combustion engine, i.e., generally a drive unit, and which is therefore to be driven in rotation around an axis of rotation A. An output region 14 of the torsional vibration damping arrangement 10 is formed with a flywheel 16 to which is connected, for example, a pressure plate assembly of a friction clutch and which can provide a friction surface 18 for a friction clutch of this kind. Two torque transmission paths 20, 22 arranged between the input region 12 and the output region 14 branch out in the input region 12 and converge in the region of a coupling arrangement which is designated generally by 24.
A phase shifter arrangement, designated generally by 26, is provided in the first torque transmission path 20. Torsional vibrations or generally rotational irregularities which are introduced into the torsional vibration damping arrangement 10 in the input region 12 and which are also partially transmitted via the first torque transmission path 20 can be shifted in phase by the phase shifter arrangement 26 with respect to the corresponding torsional vibrations or rotational irregularities, which are also contained in the torque component transmitted via the second torque transmission path 22. These two torque components with torsional vibration components, which are out of phase relative to one another, are brought together in the region of the coupling arrangement 24 so that the vibration components, which are out of phase relative to one another, ideally cancel each other so that a total torque that is substantially free from rotational irregularities and torsional vibrations is introduced into the output region 14.
The phase shifter arrangement 26 comprises a vibration system 28 with a first primary side 30 that is formed generally by two cover disk elements 32, 34. The torsional vibration damping arrangement 10 is fixedly connected to a driveshaft or the like in the region of cover disk element 32. The vibration system 28 further comprises a first secondary side 36, which is substantially provided in this case by a central disk element 38 positioned between the two cover disk elements 30, 34. A first damper element arrangement 40, which is formed by a plurality of springs, preferably helical compression springs, acts between the first primary side 30 and the first secondary side 36 and allows the latter to rotate relative to one another around the axis of rotation A while generating a restoring action.
In the radially inner region, the central disk element 38 provides a second primary side 42. A second secondary side 44, which again comprises two cover disk elements 46, 48, is associated with this second primary side 42. A second damper element arrangement 50 which, for example, again comprises a plurality of springs, e.g., helical compression springs, which are distributed in circumferential direction acts between the second primary side 42 and the second secondary side 44 so that the second primary side 42 and the second secondary side 44, are rotatable relative to one another around the axis of rotation A accompanied by the restoring action of the second damper element arrangement 50.
It will be seen that the vibration system 28 is formed with two stages with two vibration dampers acting in series and comprising the two damper element arrangements 40, 50. In so doing, the first primary side 30 substantially forms the primary side of the entire vibration system 28, i.e., that side on which the torque is introduced in the tension state, while the second secondary side 44 provides the secondary side of the entire vibration system 28, i.e., that side via which the torque is transmitted.
An essential characteristic of vibration systems of this kind is that they operate subcritically in an excitation frequency range below their natural or resonant frequency, i.e., excitation and reaction of the system at the primary side 30 on the one hand and at the secondary side 44 on the other hand take place substantially simultaneously, i.e., in the same phase without a mutual phase shift. When the resonant frequency is exceeded, the vibration system 28 passes into a supercritical state in which excitation and reaction are shifted in phase with respect to one another. Accordingly, a maximum phase shift of 180° can occur. As a result, when there are exciting frequencies in the torque received at the input region 12 which are above the resonant frequency and therefore, depending on the quality of vibration decoupling, undergo a maximum phase shift of 180° in the first torque transmission path 20 with respect to the vibration excitation components contained in the torque component of the second torque transmission path 22, there is, ideally, a complete destructive superposition of these vibration components with the in-phase vibration components in the coupling arrangement 24.
The coupling arrangement 24 comprises a planetary gear arrangement 52 with a planet wheel carrier 54. This planet wheel carrier 54 together with the primary side 30 of the vibration system 28 is connected to the driveshaft and is associated with the second torque transmission path 22. A plurality of planet wheels, designated generally by 56, are rotatably supported at the planet wheel carrier 54 so as to be distributed in a circumferential direction. For this purpose, a plurality of planet wheel carrying bolts 58 are provided at the planet wheel carrier 54, as is clearly shown in FIG. 2. The planet wheels 56 are rotatable around the rotational axes thereof, which are oriented substantially parallel to the axis of rotation A of the planet wheel carrier 54, via a bearing 60, which is formed, for example, as a needle bearing or other type of rolling element bearing. The planet wheels 56 are held so as to be axially centered between two supporting elements 62, 64 formed, e.g., as annular disks or the supporting element 64 and planet wheel carrier 54. Respective stop disks 66, 68, 70, 72, which can annularly surround the planet wheel rotational axes Z, provide for a low-friction axial support of the planet wheels 56.
The planet wheels 56 have two working toothing regions 74, 76 arranged successively in direction of the rotational axes Z of the planet wheels. Working toothing region 74, which is formed in the depicted example with greater radial dimensioning with respect to the rotational axis Z of the planet wheels, meshingly engages with a ring gear 78, which is fixed to a ring gear carrier 82 and which, for example, can have an annular or ring segment shape. The ring gear carrier 82 is in turn fixedly connected, for example, by screws, to the second secondary side 44, i.e., generally the secondary side of the vibration system 28, and is accordingly associated with the first torque transmission path 20. The torque, which is transmitted via the first torque transmission path 20 and conveyed by the vibration system 28, is introduced into the coupling arrangement 24, namely, the working toothing region 74 of the planet wheels 56, via the ring gear carrier 82 and ring gear 78. The torque transmitted via the second torque transmission path 22 is introduced into the coupling arrangement 24 via the planet wheel carrier 54 and the planet wheel carrying bolts 58. The torque components brought together in this way are conveyed as a total torque via working toothing region 76 into a ring gear 84 which has an annular or ring segment shape, for example. The ring gear 84 is connected to the flywheel 16 by screws and is accordingly associated with the output region 14.
By bringing together the two torque components of the two torque transmission paths 20, 22 in the coupling arrangement 24 formed with the planetary gear train 52, a superposition takes place when the vibration system 28 passes into the supercritical state as a result of the vibration excitation such that the vibration components are at least partially canceled and the flywheel 16 receives a substantially smoothed torque. In this respect, the magnitude of the torque components transmitted via the two torque transmission paths 20, 22 can be influenced through the choice of the diameter ratio of the two working toothing regions 74, 76 or also by means of the design of the tooth geometry of these two working toothing regions 74, 76. In the depicted example, in which the working toothing region 74 cooperating with the ring gear 78 of the first torque transmission path 20 has a greater radial dimensioning than the working toothing region cooperating with the ring gear 84 of the output region 14, a transmission ratio of i>1 is achieved, which means that a torque component is transmitted in direction of the planetary gear train 52 via each of the two torque transmission paths, and the ratio of components can be adjusted through the relative proportions or diameter ratio of the two working toothing regions 74, 76. If working toothing region 76 has a greater diameter than working toothing region 74, a torque reversal takes place in the second torque transmission path 22, whereas torque is increased in the first torque transmission path 20, so that when the torque components are brought together in the coupling arrangement 24 a total torque that corresponds to the introduced torque is achieved again, but wherein the vibration components are at least partially eliminated.
To provide this possibility of influencing the torque components transmitted via the two torque transmission paths 20, 22 through the configuration of the planet wheels 56, it is necessary to be able to configure the two working toothing regions 74, 76 independently from one another, that is, with a different diameter with respect to the planet wheel rotational axis Z and/or different toothing geometry. To this end, as is clearly shown in FIGS. 1 and 2, the planet wheels 56 can be constructed with two gearwheel parts 86, 88, wherein the first working toothing region 74, i.e., the working toothing region cooperating with the ring gear 78 of the first torque transmission path 20, is formed at the first gearwheel part 86, while the second working toothing region 76 cooperating with the output-side ring gear 84 is formed at the second gearwheel part 86. In order to achieve the combination of the two torque components described above, it is necessary that the two gearwheel parts 86, 88 are fixedly connected to one another, in particular so as to be fixed with respect to relative rotation.